VENOUS OXYGEN SATURATION AND LACTATE GRADIENT FROM SUPERIOR VENA CAVA TO PULMONARY ARTERY IN PATIENTS WITH SEPTIC SHOCK

Abstract

Monitoring of central venous oxygen saturation (S(cv)O(2)) is considered comparable with mixed venous oxygen saturation (S(v)O(2)) in the initial resuscitation phase of septic shock. Our aim was to assess their agreement in septic shock in the intensive care unit setting and the effect of a potential difference in a computed parameter, namely, oxygen consumption (VO(2)). In addition, we sought for a central venous to pulmonary artery (PA) lactate gradient. We enrolled 37 patients with septic shock who were receiving noradrenaline infusions, and their attending physicians had placed a PA catheter for fluid management. Blood samples were drawn in succession from the superior vena cava, right atrium (RA), right ventricle, and PA. Hemodynamic and treatment parameters were monitored, and data were compared by correlation and Bland-Altman analysis. Mixed venous oxygen saturation was lower than S(cv)O(2) (70.2% +/- 11.4% vs. 78.6% +/- 10.2%; P<0.001), with a bias of -8.45% and 95% limits of agreement ranging from -20.23% to 3.33%. This difference correlated significantly to the noradrenaline infusion rate and the oxygen consumption and extraction ratio. These lower S(v)O(2) values resulted in computed VO(2v) higher than the VO(2CV) (P<0.001), with a bias of 104.97 mL min(-1) and 95% limits of agreement from -4.12 to 214.07 mL min(-1). Finally, lactate concentration was higher in the superior vena cava and RA than in the PA (2.42 +/- 3.15 and 2.35 +/- 3.16 vs. 2.17 +/- 3.19 mM; P<0.01 for both comparisons). Thus, our data suggest that S(cv)O(2) and S(v)O(2) are not equivalent in intensive care unit patients with septic shock. Additionally, the substitution of S(cv)O(2) for S(v)O(2) in the calculation of VO(2) produces unacceptably large errors. Finally, the decrease in lactate between RA and PA may support the hypothesis that the mixing of RA and coronary sinus blood is at least partially responsible for the difference between S(cv)O(2) and S(v)O(2).